In general, SIR systems perform a number of functions including crash sensing, diagnostics, signal processing and analysis, and deployment of one or more restraint devices such as frontal or side air bags or seat belt pretensioners. When the system is designed such that the components for performing most or all of these functions are packaged together in single electronic module, the system architecture may be characterized as centralized. When the system is designed so that the components are separately packaged based on functionality and interconnected by a data and communication bus, the system architecture may be characterized as distributed.
The selection of centralized vs. distributed architecture depends upon a number of factors, including the number of restraint devices, controller throughput requirements, package size, system cost and assembly considerations. In relatively simple mechanizations involving a small number of restraint devices and limited sensing and processing requirements, the centralized architecture may offer cost and assembly advantages. In relatively complex mechanizations involving a large number of restraint devices and sophisticated sensing and processing requirements, the distributed architecture may offer packaging and processing advantages.
A system architecture of the centralized type is schematically represented by the block diagram of FIG. 1. Referring to FIG. 1, the centralized system comprises a high function central processor and a number of side impact sensors, occupant sensors and restraint initiator modules. The central processor includes frontal acceleration sensor(s), power supply and energy reserve devices, interface circuitry for communicating with the sensor and initiator modules, a microprocessor for processing the sensor signals and executing the deployment algorithm, diagnostic circuitry and firing circuits for each of the restraint initiators. The remote side impact sensors provide information which may be difficult to sense in a central location of the vehicle, and the remote occupant sensors provide information about occupant position that is taken into consideration by the deployment algorithm.
A system architecture of the distributed type is schematically represented by the block diagram of FIG. 2. Referring to FIG. 2, the distributed system still includes a central processor, but the sensors and initiator firing circuits (squib drivers) are packaged individually and located remote from the central processor. The role of the central processor as a communications interface now becomes more important, and other functions such as power supply and deployment control may be performed either centrally or in the remote modules, enabling the central processor to be minimized, or even up-integrated into another multi-function controller. Additionally, the flexibility of the system is increased since adding further sensors and/or initiators has only a modest impact on system cost.
Despite the many advantages of the distributed SIR system architecture, a potential disadvantage concerns the tolerance of the system to faulty modules and corrupted communication among the modules. In general, this concern increases in mechanizations where the processing functions are increasingly delegated to the remote modules, since there is no longer one central processor that has access to all possible sensor information and which is responsible for all deployment decisions.
Another potential disadvantage of a distributed SIR system architecture is that messages have to be passed very quickly over the communication bus in order to ensure that deployment of the restraint device can be initiated within 500 .mu.sec of a valid crash detection. With conventional communication protocols such as the CAN-based protocol, the required data communication rates would exceed the usual norms, ruling out the use of standard, off-the-shelf devices.